WO1998014620A1

WO1998014620A1 - Method for tanning skins

Info

Publication number: WO1998014620A1
Application number: PCT/FR1997/001754
Authority: WO
Inventors: Pierre Rigoulot
Original assignee: Beaud-Challes-Solap Sa
Priority date: 1996-10-03
Filing date: 1997-10-03
Publication date: 1998-04-09
Also published as: DE69704026T2; EP0929698B1; AU4559697A; FR2754274B1; ES2154473T3; FR2754274A1; ATE199026T1; EP0929698A1; DE69704026D1; JP2001503086A; JP3834064B2

Abstract

The invention concerns a method for tanning skins to prepare leather for use in making finished goods requiring high temperatures of the order of 80 °C for retraction of the leather. The method consists in the following steps: first, washing the skins, then submitting them to a liming operation to enable, in a subsequent skiving operation, the separation of the skins into grain leather and flesh split, the alkaline substances contained in the grain leather being eliminated by means of an acid while the flesh splits are subjected to a pickling process for softening them, then operating a step of pre-tanning previous to the shaving operation, and a step of tanning subsequent to the shaving operation, at least using in the pre-tanning operation a mixture free from chromium sulphate with a base of aldehydes, of tannin and/or of acrylic resins. The invention consists in that the mixture further contains a silica based mineral product in colloidal suspension. The invention is useful for tanning.

Description

Process for tanning skins.

The present invention relates to a process for tanning skins for the use of full-grain leathers or crusts obtained by this process in the manufacture of various products such as shoes.

The known industrial tanning processes consist of a series of operations aimed at transforming the raw natural skin of animals into leather under the chemical action of tannins or organic or mineral agents, in particular chromium salts. The objective of the tanning processes is to make the skins rot-proof and to give the leather obtained properties of mechanical resistance, in particular of resistance to temperature, suitable for the subsequent manufacturing operations. Existing tanning processes allow this optimization of the properties of leather but prove to be unfavorable to the environment due to the use of metals which are difficult to recycle or eliminate such as chromium. In addition, the use of metals such as chromium sometimes causes, due to the allergenic action of the latter, reactions in the user. In addition, in these traditional processes, tanning does not does not apply to crusts which constitute a by-product and therefore does not allow the recovery of the waste obtained after carrying out operations such as slitting and declutching.

In order to overcome the aforementioned drawbacks, there has been proposed in FR-A-2 711 145, a process for tanning skins excluding any use of chromium so as to allow on the one hand the application of the process to crusts, on the other hand the recovery of waste obtained after declutching from crusts or full-grain leathers.

However, despite the advantages of this process, it has been found that the shrinkage temperature of the leathers obtained by this tanning process is lower than that of the leathers treated by a chromium tanning process, which could cause problems with the leather's behavior. at the temperature during the stages of manufacture of the finished products and in particular for the manufacture of footwear.

In order to overcome this drawback, the present invention proposes to improve this type of chromium-free tanning process so as to increase the shrinkage temperature of the treated leathers.

To this end, the invention relates to a process for tanning skins for the preparation of leathers used for the manufacture of finished products requiring high shrinkage temperatures for leathers, in particular of the order of 80 ° C., of the type consisting before washing, washing the skins in a first step, called quenching, then subjecting them to a skinning operation to allow, in a subsequent slitting operation, the separation of the skins from leather on the flower side called leather thereafter leather and leather on the flesh side called crust, alkaline substances such as fatty lime contained in flower leathers being eliminated by neutralization by means of an acid during a so-called deliming operation while the crusts are subjected to a pickling action in order to allow their softening, then to carry out the subsequent tanning operation in two stages, said operation comprising a step of pre-tanning prior to the declutching operation known per se and a tanning step subsequent to the declutching operation known per se, at least said pre-tanning stage consisting in subjecting pickled crusts or loose hides to the chemical action of '' a mixture free of chromium sulphate based on aldehydes, tannins and / or acrylic resins, characterized in that the mixture comprises, in addition, an inorganic product based on silica in colloidal suspension.

Thus, it has been observed that the introduction of a mineral product based on silica in colloidal suspension during the pre-tanning makes it possible to obtain leathers treated by the process of the invention whose shrinkage temperature is increased compared to the leathers treated by the previous chromium-free process.

The properties of tanning agents of silica-based compounds such as aluminosilicates are known, which are used in tanning processes for the manufacture of leather and allow partial or total replacement of the auxiliaries which heavily load the factory waste water.

Thus, it has been proposed to use, as sole tanning agent, aluminum silicates (US Pat. No. 2,395,472) in an acid medium to which organic donor compounds fixing hydrogen are added such as ethers, amides, alcohols, ketones and phosphoric acid esters so as to avoid any difficulties in an acid medium. These additions complicate the process and make it expensive so that it could not be implemented industrially. Patent EP-B-0 005 546, for its part, proposed to reduce the use of commonly used heavily loaded auxiliaries, in particular chrome tanning materials, by recommending the use of water-insoluble aluminosilicates in combination with di- and / or tricarboxylic acids and / or their partial esters in chrome tanning or in combination tanning with chrome, aluminum and silicon tanning materials. This use of aluminosilicates in combination with di- and / or tricarboxylic acids promotes an economy of the chromium tanning process and a reduction in the burden on the environment.

The tanning described in this patent is carried out in the usual manner, the pickling and tanning can be combined in a manner known per se and then the leather is lubricated. About 10 to 50 g are used per liter of aluminum silicate calculated as an anhydrous product in the tanning bath and the acids used are brought into the tanning bath in an amount of 1 to 20 g per liter.

Of course, the usual active and auxiliary substances such as anionic, cationic or nonionic surfactants, chromium salts, etc. are also used. The aluminum silicates used during the process are generally in a crystalline or amorphous form, can be synthetic or natural, directly prepared or obtained commercially and preferably have at least partial acid solubility in pH range 2.5 to 5 and preferably 3.5 to 4.5.

Patent EP-B-0 007 555 proposes a tanning process recommending the use of water-insoluble aluminosilicates in combination with carboxylic acids containing ester and / or urethane and / or amide groups in chromium tanning or tanning combined with chrome, aluminum and silicon tannins that provide also the same advantages as the process described in EP-B-0 005 546.

However, despite a drop in the load of pollutants, the latter two methods still use said pollutants, in particular chromium.

In order to overcome these drawbacks of the processes mentioned, according to the process of the present invention, during the pretanning stage, a mixture, free of chromium sulphate, based on aldehydes, tannins and / or resins is introduced. acrylic and which also comprises a mineral product based on silica, so as to obtain leathers treated without the use of chromium having an increased shrinkage temperature compared to leathers treated simply by the mixture free of chromium sulphate and this, unexpectedly.

Preferably, the mineral product based on silica in colloidal suspension is presented as a colloidal suspension of amorphous silica.

The invention also relates to a leather obtained by the implementation of the method, characterized in that it is composed of the flesh side or the flower side of a skin.

Other characteristics and advantages of the invention will become apparent on reading the description which follows and the attached single figure which represents a block diagram of the process which is the subject of the invention.

In accordance with the diagram represented in the single figure, the first operations implemented on a rawhide bought in hair consist of washing and then depilating the skins in order to allow their slitting, that is to say the separation of the skin tripe in two parts, one side said flesh side also called crust, the other side said flower side called leather flower. Step 1 groups these operations under the terms quenching, skinning and slitting. The quenching operation therefore consists in washing the skin. Once washed, this skin is subjected to a skinning operation which consists in carrying out, simultaneously or after the depilation, an alkaline treatment, for example, so as to cause a controlled hydrolysis of the skin in order to make the skin more receptive to subsequent operations, in particular after its separation during the slitting operation, using a lime milk H) oily.

We will first deal with the future of grain leather. The grain leather is first subjected to a deliming operation in step 2. Deliming consists in fact of an action

15 neutralization, by an acid, of the lime contained in the skin so as to remove the alkaline substances retained by the skin in guts. Once this operation has been carried out, the grain leather is subjected to a step 3 which consists of a pre-tanning of the loose grain leather. 0

This pre-tanning step is carried out by means of a mixture based on aldehydes, acrylic resin and / or synthetic or organic tannins further comprising an inorganic product based on silica in colloidal suspension. 5

Preferably, a colloidal suspension of amorphous silica containing 30% SiO 2 stabilized in an alkaline medium is used in the pH range from 10 to 10.5.

0 Preferably, the silica in colloidal suspension is provided in a proportion of 2 to 4% by weight relative to the resold weight and the diameter of the silica particles in colloidal suspension is less than or equal to 10.10 ^{~ 6} mm so as to allow better penetration of the leather. _t

In step 4, the leathers thus obtained are wrung out and, in the subsequent step, in this case step 5, a new slitting of the grain leather known as white slitting is carried out.

Then, in a step 6, the leathers thus obtained are sorted and, in a step 7, a declutching operation is carried out. In this step, the thickness of the leather is equalized so as to make this thickness uniform. Generally, this equalization is done by eliminating fine chips on the flesh side.

In order to make this waste usable, in particular as fertilizer for agriculture, the shifting machine is modified by reducing the speed of rotation of the blades. Thus, during declutching, the speed of rotation of the blades is reduced by 40 to 60%, preferably 50% compared to the speed adopted in conventional tanning processes, in particular those using chromium.

After the declutching which makes it possible to obtain recoverable waste, in a step 8, the actual tanning operation of the grain leather is carried out. Again, this tanning operation uses a chemical solution based on aldehydes, synthetic tannins and / or preferably acrylic resins.

In a subsequent step called step 9, the leather is neutralized by means of an appropriate chemical solution then again, in the next step numbered 10, a retanning operation is carried out using a solution of composition similar to that of step 8.

During retanning, a solution of products based on sodium silico-aluminates is introduced as an inerting agent. Preferably, the addition of the inerting agent is 3 to 5% of the derailed weight and said solution comprises 73 to 78% of Si0 ₂ . This solution comprising inerting agents contributes to improving the mechanical characteristics of the leather and, in particular, allows the leather to better withstand the stresses imposed during the injection of a sole onto a upper made from this leather.

Then it is possible, optionally in a step 11, to dye the leather and, in a step 12, to carry out a feeding operation, steps 11 and 12 being operations of finishing the leather.

The crusts can be treated in a similar way to grain leather as it appears on the diagram. Indeed, the split crusts can, if they undergo a pickling operation, be subsequently treated by means of operations in accordance with steps 3 to 12 of the process applied to grain leather. Again, in step 7 consisting of the declutching step, the waste obtained can be recovered. 0

Thus, not only does the process of the invention make it possible to increase the shrinkage temperature of the treated leathers but, moreover, it makes it possible to improve the properties of the treated leather while promoting the production of waste 5 usable in other fields .

Claims

1. Process for tanning hides and skins for the preparation of leathers used for the manufacture of finished products requiring high shrinkage temperatures of leathers of the order of 80 ° C., of the type consisting, before tanning, of washing the skins in a first step, called quenching, and then subject them to a skinning operation to allow, in a subsequent slitting operation, the separation of skins in leather on the grain side called grain leather and in leather side flesh called crust, the substances alkalines such as fatty lime contained in flower leathers being eliminated by neutralization by means of an acid during a so-called deliming operation while the crusts are subjected to a pickling action in order to allow their softening, then perform the subsequent tanning operation in two stages, said operation comprising a pre-tanning step prior to the declutching operation known per se, u ne tanning step subsequent to the declutching operation known per se, at least said pre-tanning step consisting in subjecting pickled crusts or loose hides to the chemical action of a mixture free of chromium sulfate based on aldehydes, tannins and / or acrylic resins, characterized in that the mixture also comprises an inorganic product based on silica in colloidal suspension.

2. Method according to claim 1, characterized in that the silica in colloidal suspension is provided in a proportion of 2 to 4% by weight relative to the resold weight.

3. Method according to one of claims 1 and 2, characterized in that the diameter of the silica particles in colloidal suspension is less than or equal to 10.10 ^-6 mm.

4. Method according to one of claims 1 to 3, characterized in that a colloidal suspension of amorphous silica containing 30% Siθ2 stabilized in an alkaline medium is used in the pH range from 10 to 10.5.

5. Method according to one of claims 1 to 4, characterized in that in the case of floral leathers, prior to stripping and after deliming, the leather is subjected after the pre-tanning step to the successive wringing operations, slitting and sorting.

6. Method according to one of claims 1 to 4, characterized in that, after the tanning step, the flower leathers and the crusts are respectively subjected successively to neutralization, retanning, dyeing and food operations. .

7. Method according to claim 6, characterized in that, during the retanning step, a solution based on sodium silico-aluminate is introduced as an inerting agent.

8. Method according to claim 7, characterized in that said solution comprises 73 to 78% of Si0 ₂ .

9. Method according to one of claims 7 and 8, characterized in that said solution is provided in a proportion of 3 to 5% of the derailed weight.

10. Method according to one of claims 1 to 9, characterized in that, during the declutching, the speed of rotation of the blades is reduced from 40 to 60%, preferably 50%.

11. Leather obtained by the implementation of a process according to claims 1 to 10, characterized in that it is composed of the flesh side or the flower side of a skin and that it is free of chromium salts .